Crumbling "Abbey": "Downton's season finale shows why the beloved series is in need of triage.

Photo: Erick Wong

Crumbling "Abbey": "Downton's season finale shows why the beloved...

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Joanne Froggatt as Anna Bates and Raquel Cassidy as Baxter.

Photo: Nick Briggs, PBS

Joanne Froggatt as Anna Bates and Raquel Cassidy as Baxter.

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Shown from left to right: Robert James-Collier as Thomas and Raquel Cassidy as Baxter.

Photo: Nick Briggs, PBS

Shown from left to right: Robert James-Collier as Thomas and Raquel...

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Lily James as Lady Rose.

Photo: Nick Briggs, PBS

Lily James as Lady Rose.

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This photo released by PBS and Carnival Film and Television Limited shows, from left, Michelle Dockery as Lady Mary, and Joanne Froggatt as Anna Bates, in a scene from season four of the Masterpiece TV series, "Downton Abbey."

Photo: Nick Briggs, Associated Press

This photo released by PBS and Carnival Film and Television Limited...

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This photo released by PBS and Carnival Film and Television Limited shows Charles Edwards as Michael Gregson and Laura Carmichael as Lady Edith in a scene from season four of the Masterpiece TV series, "Downton Abbey."

Photo: Nick Briggs, Associated Press

This photo released by PBS and Carnival Film and Television Limited...

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This photo released by PBS and Carnival Film and Television Limited shows, from left, Lesley Nicol as Mrs. Patmore, and Sophie McShera as Daisy, in a scene from season four of the Masterpiece TV series, "Downton Abbey."

Photo: Nick Briggs, Associated Press

This photo released by PBS and Carnival Film and Television Limited...

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This photo released by PBS and Carnival Film and Television Limited shows Michelle Dockery as Lady Mary in a scene from the Masterpiece TV series, "Downton Abbey." As it returns Sunday, Jan. 5, 2014, for its much-awaited fourth season, "Downton Abbey" remains a series about elegance, tradition and gentility, and the pressures of preserving them. (AP Photo/PBS/Masterpiece, Nick Briggs)

Photo: Nick Briggs, Associated Press

This photo released by PBS and Carnival Film and Television Limited...

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This photo released by PBS and Carnival Film and Television Limited shows Rob James-Collier as Thomas in a scene from season four of the Masterpiece TV series, "Downton Abbey."

Photo: Nick Briggs, Associated Press

This photo released by PBS and Carnival Film and Television Limited...

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This photo released by PBS and Carnival Film and Television Limited shows Tom Cullen as Lord Gillingham in a scene from season four of the Masterpiece TV series, "Downton Abbey." As it returns for its much-awaited fourth season, it remains a series about elegance, tradition and gentility, and the pressures of preserving them.

Photo: Nick Briggs, Associated Press

This photo released by PBS and Carnival Film and Television Limited...

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This photo released by PBS and Carnival Film and Television Limited shows Gary Carr as Jack Ross in a scene from season four of the Masterpiece TV series, "Downton Abbey."

Photo: Nick Briggs, Associated Press

This photo released by PBS and Carnival Film and Television Limited...

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This photo released by PBS and Carnival Film and Television Limited shows Laura Carmichael as Lady Edith in a scene from season four of the Masterpiece TV series, "Downton Abbey."

Photo: Nick Briggs, Associated Press

This photo released by PBS and Carnival Film and Television Limited...

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Fans of 'Downton Abbey' were devastated when moments after meeting his newborn son, heir to the estate, Matthew Crawley, is in a car accident and dies. Some viewers claimed that his death, which occurred in the 'Downtown Abbey' Christmas episode, ruined the holiday for them.

Fans of 'Downton Abbey' were devastated when moments after meeting...

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'Downton Abbey' fans were outraged and left broken-hearted when Sybil, the youngest Crawley daughter, died from eclampsia shortly after giving birth to her daughter.

It's time to stop being polite about what's going on with "Downton Abbey." The fourth season, which comes to a close Sunday night, has had some nice moments, but the increasing weakness of creator Julian Fellowes' writing skills is harming the series, especially in comparison to its first season.

PBS always sends the entire series to TV critics, except for the last episode. Last year, that was to ensure that we didn't tell you about Matthew Crawley's death. This year, the "Christmas episode" also has something they don't want us to tell you: It's just plain dopey and the series is in trouble.

While the episode continues plot strands from the rest of the season, the main story is something out of either a French farce, a '30s American screwball comedy or the Three Stooges - take your pick, depending on how irritated you are about how much the show's quality has slipped.

Amid all the usual sighs and whispers of class coexistence, we suddenly find a handful of major characters - from upstairs as well as down - absconding with our attention as they conspire to get a potentially dangerous letter out of the hands of a sleazy minor character. With even less plausibility than we've had to get used to all season, the co-conspirators hatch a ridiculously farcical scheme that occupies much of the finale episode.

Once again, Fellowes shows little respect for the characters he's created and, for the sake of cheap entertainment, I suppose, cooks up an absurd plot device to keep us from falling asleep.

When the new season started, my take was that it was still entertaining but that I was disappointed that the characters were being undervalued in the script. By that I meant that Fellowes increasingly manipulates characters to do things that are not true to who they are. I won't even get into the fact that no one seems able to have a conversation without someone else conveniently overhearing it, but more and more, convenience in general is ruining "Downton Abbey."

The season finale goes beyond that, though, achieving a new level of implausibility. By disrespecting his characters as much as Fellowes does, he is disrespecting the fan base "Downton" has built over four seasons. We've developed interest and even affection for the characters, but by batting them about with amateur abandon, as he does with increasing frequency, Fellowes is taking his audience for granted. Viewers deserve better.

The hissing interplay between Smith and MacLaine is amusing and not unwelcome. But it's also pure pandering to the fan base. In the ever-expanding gallery of Julian Fellowes' cheap tricks, it's far from the worst offender.

"Downton Abbey" is in need of a good housecleaning, upstairs and down - not to get rid of any cast members (several have already seen the cliche-ridden handwriting on the wall and have bolted) but to restore the series to what it was at the beginning and what its loyal fans deserve.